Roof Ventilation

[Doug71]

I am trying to sort out a few damp problems in my mothers house and when I was up in the loft I realised the loft space isn't vented and there are definite signs of condensation up there.

It's a straight traditional pitch roof with a solid 9" brick gable at each end, only about 5 m long and probably 7 m deep (length of gable end). It was re roofed probably 40 years ago with flat concrete tiles and traditional felt, it's a typical cold roof space with fibreglass insulation laid over the ceiling and joist. There are fascia boards front and back which I think the tiles just sit on.

What is the best way to vent it? I have seen the vent type tiles (I presume you need to cut the felt underneath them?) or should we put some vent bricks in the gables, is one way better than the other? How many are needed and where should they go?

I have a roofer coming on Monday to look at the flashing round a chimney so was going to ask his opinion but thought I would run it past you knowledgeable people first.

Many thanks, Doug

 

[MikeG.]

BBQ-ing...I've only got a minute.

The best answer involves cross ventilation. In other words, do both eaves, or both gables (there are two gables??). Messing with the eaves is a nightmare, so actually the most pragmatic solution is normally some big vents in the gables.

 

[Robbo3]

When our loft was insulated some 10 years ago the chaps that did it also installed about 10 gadgets that hold the felt overlap open. They consist of two layers of thin rigid plastic, stapled at both ends & 2 springs between the layers, When inserted in the felt overlap the springs create an opening to allow air in. I have to reinsert them occasionally when the wind causes them to work their way out.

 

[owen]

If you have a roofer coming just get him to fit a few tile vents while he's there. They don't take long to fit, certainly quicker than making holes in the gable ends for brick vents

 

[Woody2Shoes]

Another thing to check would be to make sure that there is no route for warmer moister air from the rooms downstairs into the loftspace esp. any penetrations (even for wires or pipwork) through the ceiling of bathroom or kitchen. My mum's place had the hose from her bathroom extractor just sitting and terminating on the rockwool insulation they were too lazy to vent the outside!